Aligning components of a measuring system

ABSTRACT

A measuring system for calibrating a machine in which a base ( 10 ) is attachable to a surface of the machine and a housing ( 20 ) is mountable on the base, wherein at least one surface of the base and at least one surface of the housing are each provided with a complementary part of a mounting device, such that when the two parts of the mounting device are connected together, the housing may be aligned in any of a plurality of predetermined directions. The base includes a lifting mechanism ( 64 ) which when lowered allows the complementary parts of the mounting device ( 93, 95 ) of the housing ( 20 ) and the base ( 10 ) to be in contact and when raised causes them to at least partly break contact with one another. The level of the base ( 10 ) may be adjusted using a system of members and tapered rollers.

This is a Continuation of application Ser. No. 10/501,475 filed Jul. 14,2004 (now U.S. Pat. No. 7,168,290), which in turn is a National Stage ofPCT/GB03/00175 filed Jan. 16, 2003. The disclosure of the priorapplication is hereby incorporated by reference herein in its entirety.

BACKGROUND

The present invention relates to a method of and apparatus for aligningthe components of an optical measuring system preparatory to using themin a measuring operation.

One known type of optical measuring system consists of two or morehousings, at least one of which is to be fixed to the bed of the machineand another one of which is to be carried by the arm or spindle of themachine. Either one or both of the machine bed and machine spindle ismovable. One of the housings contains one or more light sources anddetectors, and will be referred to hereinafter as the “source housing”while the other housing contains reflectors, and will be referred tohereinafter as the “reflector housing”. Usually the source housing ismaintained in a fixed position on the bed of the machine and thereflector housing is mounted on a part of the machine moveable withrespect to the machine bed e.g. the machine spindle.

Aligning the optical components is often a time-consuming process whichinvolves firstly the alignment of the source housing so that the beam orbeams generated are directed along, or parallel to, one or more of theX, Y and Z axes of the machine. Then the reflectors have to be alignedwith the beam or beams so that the reflected beams are directed backonto the detectors. Depending on the type of detectors being used thealignment may have to be accurate to within a few arc seconds.

SUMMARY

A first aspect of the invention provides a measuring system forcalibrating a machine, the measuring system comprising:

-   -   a base attachable to a surface of the machine:    -   a housing mountable on the base;    -   wherein at least one surface of the base and at least one        surface of the housing are each provided with a complementary        part of a mounting device, such that when the two parts of the        mounting device are connected together, the housing may be        aligned in any of a plurality of predetermined directions.

Preferably the measuring system has at least two housings, comprising:

-   -   a base attachable to a first surface of the machine on which a        first housing may be mounted;    -   a second housing attachable to a second surface on the machine,        said first and second surfaces of the machine being moveable        relative to one another;    -   said first and second housings each being provided with a        complementary part of a first mounting device, such that when        the two parts of the first mounting device are connected        together, the housings are mutually aligned;    -   wherein at least one surface of the base and at least one        surface of the first housing are each provided with a        complementary part of a second mounting device, such that when        the two parts of the second mounting device are connected        together, the first and second housings may be aligned in any of        a plurality of predetermined directions.

The complementary parts of the second mounting device may comprise a setof cooperating elements on the base and the first housing. A subset ofcooperating elements used to align the first housing in a firstdirection may also form a subset of cooperating elements used to alignthe first housing in a second direction.

Preferably the second housing is mounted onto the second surface of themachine via a connecting device and wherein a plurality of surfaces onthe second housing and at least one surface on the connecting device areeach provided with a complementary part of a third mounting device, suchthat the second housing may be attached to the connecting device whenorientated in any of the plurality of predetermined directions

The complementary parts of the third mounting device may be arrangedsuch that once the first and second housings have been aligned using thefirst mounting device, and the first housing and base have been alignedusing the second mounting device, the second housing and the connectingdevice may be connected without realignment of the first and secondhousing relative to one another being required.

Preferably the geometric combination of the first and second housingsand the connecting device is such that the axes along which the firstand second housings may be aligned intercept at a common point. This maybe such that the housing mounted on the moving part of the machinestarts in the same position in X, Y and Z whatever the orientation ofthe first and second housings. Alternatively it may be such that thehousing mounted on the moving part of the machine is moved through thecommon point of interception, whatever the orientation of the first andsecond housings.

A cable leads to the first housing and the cable may be provided with acable mounting device, and the at least one surface on the cablemounting device and a plurality of surfaces on the base are eachprovided with complementary parts of a fourth mounting device such thatthe cable mounting device may be mounted on the base at differentlocations such that at each orientation of the first housing, the cabletransmits an equal force on the housing. The cable mounting device maybe provided with a plurality of angled faces, wherein two or more facesof the cable mounting device are provided with said complementary partof the fourth mounting device, such that different faces of the cablemounting device may be attached to base for different orientations ofthe first housing, such that the cable transmits an equal force on thehousing for each orientation of the housing.

A second aspect of the invention provides a platform for supporting ahousing, the housing and platform being provided with complementaryparts of a mounting device which define the position of the housing whenmounted on the platform, comprising:

-   -   a fixed surface of the platform on which the housing may be        supported and on which part of said mounting device is located;    -   a lifting mechanism moveable between upper and lower positions        relative to said fixed surface;    -   whereby in its lower position, the lifting mechanism allows the        complementary parts of the mounting device of the housing and        the fixed surface to be in contact with one another and in its        upper position, the lifting mechanism causes the complementary        parts of the mounting device of the housing and the fixed        surface to at least partly break contact with one another.

Preferably the lifting mechanism comprises a movable surface of theplatform which may be raised and lowered;

-   -   whereby when the housing is placed on the moveable surface of        the platform, the moveable surface may be lowered to place the        housing onto the fixed surface such that the complementary parts        of the mounting device are connected or raised to disconnect the        complementary parts of the mounting device.

The movable surface and the housing may be provided with complementaryparts of a second mounting device such that the complementary parts ofthe first mounting device on the housing and fixed surface are therebypre-aligned.

In a first embodiment, rotation of the movable surface in a firstdirection causes said movable surface to be raised and wherein rotationof the movable surface in a second opposite direction causes saidmovable surface to be lowered.

In a second embodiment the movable surface is mounted on a springwhereby rotation of a cam raises or lowers the spring and thus themovable surface.

A third aspect of the invention provides apparatus for adjusting theangle of an object about an axis mounted on a surface comprising:

-   -   an upper plate onto which the object is mounted and a lower        plate which in turn is mounted onto the surface;    -   a track located on the inner surface of one of the upper and        lower plates;    -   a ball located between the upper and lower plates, the ball        being in contact with the at least one track in the upper or        lower plates;    -   wherein the track is arranged such that when the ball is moved        in a first direction, the ball is raised and causes the plates        to move apart and wherein when the ball is moved in a second        opposite direction, the ball is lowered and causes the plates to        move together.

The track may comprise a pair of non-parallel rollers. Alternatively,the track may comprise a pair of parallel rollers which are positionedat an angle from the plane of the upper or lower plate in which they arelocated, or a pair of rollers and wherein each roller in the pair ofrollers is tapered.

Preferably the other of the upper and lower plates is provided with atleast one element which is in contact with the ball. The at least oneelement may comprise a pair of parallel rollers. Alternatively, the atleast one element may comprise a plane surface.

Preferably one of the at least one element and the track in the upperplate is part of a mount for the object and the other of the track andthe at least one element of the lower plate is part of a mount for thesurface, thereby forming a direct path from the object to the surfacethrough the tracks, balls and elements.

In a preferred embodiment, several sets of balls and tracks are providedso that the angle of the upper plate may be adjusted about several axes.In addition, a track and ball may be provided between adjacentsubstantially vertical surfaces of the upper and lower plates such thatthe upper plate may be rotated about the axis perpendicular to the planeof the lower plate.

Preferably the apparatus is provided with at least two tracks and ballsto adjust the angle of the upper plate relative to the plane of thelower plate and one track and ball to adjust the angle of the upperplate about the axis perpendicular to the plane of the lower plate,wherein the tracks used to adjust the angle of the upper plate relativeto the plane of the lower plate are located in the lower plate so thatduring rotation of the upper plate, the elements in the upper plate mayslide or rotate over the balls and thereby allow the upper plate to berotated independently of the adjustment of the angle of the upper platerelative to the plane of the lower plate.

Two sets of tracks and rollers and a pivot may be provided to allowadjustment of the angle of the upper plate relative to the plane of thelower plate. In addition, a third set of track and roller may beprovided to provide rotation of the upper plate about an axisperpendicular to the plane of the lower plate.

Three sets of tracks and rollers may be provided to allow adjustment ofthe angle of the upper plate relative to the plane of the lower plateand in addition allow adjustment of the height of the upper platerelative to the lower plate. A fourth set of tracks and rollers may beprovided to provide rotation of the upper plate about an axisperpendicular to the plane of the lower plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, and withreference to the following drawings in which:

FIG. 1 is a diagrammatic elevation of the component of a prior artoptical measuring system;

FIG. 2 is a side view of an adjustable connector according to theinvention;

FIGS. 3A-3E are views of the source and reflector housings aligned alongthe X, Y, -X, -Y and Z axis directions;

FIGS. 4A and 4B show the geometric combination of the source andreflector housings aligned along the Y and Z directions;

FIGS. 4C and 4D illustrate the interception of axes for differentorientations of the housings;

FIG. 4E illustrates the errors along the X direction for FIG. 4D;

FIG. 5A is a plan view of the optical measuring system aligned with theZ axis;

FIG. 5B is a side view of the optical measuring system aligned with theZ axis;

FIG. 5C is a plan view of the optical measuring system aligned with theX axis;

FIG. 5D is a side view of the optical measuring system aligned with theX axis;

FIGS. 6A and 6B show plan and side views of a first embodiment of thecontrolled lowering platform;

FIGS. 6C and 6D show plan and side views of a second embodiment of thecontrolled lowering platform;

FIGS. 6E-6G show plan, side and perspective views of a third embodimentof the controlled lowering platform;

FIG. 6H illustrates a side view of the controlled lowering platform;

FIGS. 7-9 illustrate plan, side and perspective views of the base plate;

FIG. 10 is a cross section of the first tilt adjustment device;

FIG. 11 is a cross section of the second tilt adjustment device;

FIG. 12 is a cross section of the third location;

FIG. 13 is a cross section of the rotation adjustment device;

FIG. 14 is a schematic illustration of relative movement of the upperplate of the base plate;

FIG. 15 is a plan and side view of non-parallel rollers;

FIG. 16 is a plan and side view of parallel angled rollers;

FIG. 17 is a plan and side view of tapered rollers;

FIG. 18 is a plan view of a biasing spring used in the base plate ofFIGS. 7-9;

FIG. 19 is a side view of the biasing spring of FIG. 18;

FIG. 20 is a perspective view of the biasing spring of FIG. 18; and

FIG. 21 is a schematic illustration of the arrangement of kinematicelements in a prior art base plate.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to the drawings, FIG. 1 shows a prior art embodiment of anoptical measuring system for mounting on a machine as disclosed inco-pending application PCT/GB01/03096 filed on 11 Jul. 2001.

The optical measuring system includes a base plate 10, a source housing20 and a reflector housing 22, all of which need to be properly alignedwith one or more of the machine axes. The base plate 10 is connected tothe bed of the machine by screws 12, 14.

The source housing 20 may contain an autocollimator formed in opticalsequence by, a light source 24, a beam splitter 26, a collimating lens28 through which a collimated light beam passes out of the housing, anda detector 30 which receives a return light beam from the reflector 32in the reflector housing 22 via the beam splitter 26.

The source housing 20 also includes a kinematic seat in the form ofthree cooperating pairs of male and female elements, for example a balland V-groove 16, suitably spaced and arranged in a triangular array, forexample spaced at 120° apart. The seating elements 16 cooperate withthree V-shaped grooves (not shown) on the base plate to form aconventional kinematic seat for repeatable positioning of the housing onthe base plate.

The source housing has a further kinematic seat 18 on its front face(i.e. the face which is orthogonal to the beam direction) on which thereflector housing may be seated. The light source and the reflector arealigned during the manufacturing stage to ensure that when the reflectorhousing is seated in the kinematic seat 18 on the front fact of thehousing, the light beam and reflector are properly aligned.

It can be seen therefore that once the source housing 20 is correctlyaligned to direct a light beam along one of the machine axes, eg theX-axis, the reflector housing 22 can be seated on the kinematic seat 18on the front face of the source housing 20, and will automatically bealigned with the beam from the light source 24. Magnets 33 may be usedto urge the two housings 20, 22 together at the kinematic seat 18.

In order to take care of any mis-match in position between the machinespindle 34 and the reflector housing 22 when the two are to be connectedtogether, the reflector housing 22 is provided with a limited amount ofcompliance by using an adjustable connector by means of which thehousing 22 can be connected to the spindle 34 of the machine. Theadjustable connector has a ball 36 which is to be seated in a socket 38on the machine spindle. The ball 36 is adjustably supported in aretaining device 40 which, in turn is connected to the reflector housing22, by any suitable means.

A preferred embodiment of the adjustable connector will now be describedwith reference to FIG. 2. The socket 38 of the machine spindle comprisesa cylindrical bore which houses ball 36 of the adjustable connector. Theretaining device 40 also comprises a cylindrical bore 42 and is mountedon the reflector housing 22, preferably by kinematic mounts 52.

The ball 36 of the adjustable connector is connected by a stem 46 to afurther ball 48 which lies inside the bore 42 of the retaining device40.

The Balls 36 and 48 of the adjustable connector may only have a partspherical surface at the portion of the ball in contact with the surfaceof the cylindrical bore.

The ball 36 can be adjusted through a limited angle to enable it to beengaged in the socket 38 of the machine spindle. The ball is retained insocket 38 in known manner by providing magnets (not shown) in the ball36, the socket 38, or both.

Two slits 54, 56 extends from opposite ends of the adjustable connectoralong its longitudinal axis to just short of its center, leaving just asmall bridging portion 57 connecting the two halves of the adjustableconnector together. A locking screw 58 is provided in the socket 38 ofthe machine spindle which when tightened pushes against the ball 36,thus fixing the ball 36 within the socket 38 and also pushing the twohalves of the ball 36 together. The bridging portion 57 of theadjustable connector acts as a hinge and as the two halves of ball 36are pushed together, the two halves of ball 48 are pushed apart andagainst the sides of the cylindrical bore 42, fixing it in position.

This connector thus has the advantage that one actuation locks bothballs.

Once the source housing 20 has been aligned with an axis of the machine,the reflector housing 22 attached to the machine spindle can be broughtup to the source housing 20. With the locking screw loosened, theadjustable connector will be free enough to rotate so that the reflectorhousing 22 will seat in the kinematic seat 18. By this means automaticalignment of the source housing 20 and the reflector housing 22 can beensured. Once seated in the kinematic seat 18 the locking screw istightened to maintain the orientation of the housing 22.

It is desirable to align the source housing 20 with other machine axes.In the above-described example, where the source housing is mounted on abase plate, the source housing may have other sets of kinematic elementson its lower surface or on other ones of its orthogonal faces. By thismeans it can be rotated through 90° in different planes and be re-seatedon the kinematic seat on the base plate in different orientations withthe light beam from the source directed along different ones of themachine axes. The reflector housing will continue to seat in the samekinematic seat 18 on the source housing so that it will also be alignedwith the different axes.

FIGS. 3A-D show the plan view of the source housing 20 and reflectorhousing 22 on the base plate 10. FIG. 3 a shows the light beam alignedwith the X axis, FIG. 3 b shows the light beam aligned with the Y axis,FIG. 3 c shows the light beam aligned with the -X axis and FIG. 3 dshows the light beam aligned with the -Y axis. FIG. 3 e shows a sideview with the light beam aligned with the Z axis.

A set of kinematics elements are provided on the base plate and sourcehousing to define each of the X, Y, Z, -X, -Y directions. Each set ofkinematics are not necessarily independent, with balls and rollers orV-shaped grooves from one set also forming part of another set.

Alternatively a block in the form of a cube or a cuboid may be usedinstead of a base plate. Such a block would be provided with kinematicseats on various ones of its orthogonal faces so that, by using a singlekinematic seat on the source housing, it can be oriented in differentdirections by engaging its kinematic seat with any one of those on theblock. Also in this case the reflector housing will continue to use thesame kinematic seat on the source housing.

For each orientation of the source and reflector housing 20, 22, thereflector housing 22 must be mounted on the retaining device 40 of theadjustable connector in a different position. The location of thereflector housing 22 on the retaining device 40 for each orientation isdefined by a respective kinematic seat. A different set of kinematicelements is thus provided between the reflector housing 22 and theretaining device 40 for each orientation of the reflector housing. Asbefore, each set of kinematics may share elements with another set. Thisenables the orientation of the reflector housing 22 to be changedwithout adjustment of the adjustable connector in the machine spindle.

Once the source and reflector housings 20, 22 have been aligned for thefirst axis using the kinematic seat 18, the orientations of thekinematic elements between the source housing 20 and the base plate 10and between the reflector housing 22 and the retaining device 40 meansthat for subsequent axes, realignment of the source and reflectorhousings 20, 22 on the kinematic seat 18 is not required.

For calibration of large machines, it is desirable to start with thesource housing 20 in the middle of the machine and first move thereflector housing 22 along one axis (e.g. X axis) and then turn thesource and reflector housings 20, 22 around 180° and move the reflectorhousing along that axis in the opposite direction (e.g. -X axis). It isthus desirable for the source housing 20 and base plate 10 to havekinematics defining the -X and -Y directions.

There are thus five sets of kinematics between the source housing 20 andthe base plate 10 and between the reflector housing 22 and the retainingdevice 40 defining the X, Y, Z, -X and -Y directions, although each setis not necessarily independent from the other sets.

As illustrated in FIGS. 4A and 4B, the geometric combination of thesource housing 20 and the reflector housing 22 allow the sameco-ordinate start position for calibration of x, y and z axis afterinitial set up.

FIG. 4A shows the source housing 20 being aligned along the Y axis andFIG. 4B shows the source housing 20 aligned along the Z axis. In bothcases the distance a between the quill 34 and the reflector housing 22is the same. Thus when calibrating in different orientations (i.e. alongthe X, Y or Z axes), the start point is always the same.

As illustrated in FIG. 4C, the geometric combination of the sourcehousing 20 and the reflector housing 22 is such that there is aninterception of the axes (X, Y, Z) along which the source and reflectorhousings are to be aligned. Preferably the co-ordinate start position isat this interception O (as described above). However it is also possibleto have non-common start positions, a1, b1, c1 for each orientation, aslong as there is an interception of the axes and the distance xa, xb, xcbetween each start point a1, b1, c1 and the interception 0 is known.(Although these distances do not need to be known accurately). In thiscase, it is preferable that the start points are on the far side of theinterception from the direction of travel, as illustrated in FIG. 4C, asthis results in no loss of information during movement of the reflectorhousing. As illustrated in FIG. 4D, this would not be the case if thestart positions a2, b2, c2 are on the other side of the interception Oas there will be no data between the interception and the startpositions a2, b2, c2 which will introduce errors. FIG. 4E shows themeasurement data along the X axis for the arrangement of FIG. 4D. Thereis no information between the origin O and the start point a2.

The optical source may be located remotely from the source housing,particularly as heat from the optical source may cause distortion on thehousing. An optical fiber may thus be used to channel the light from thelight source to the source housing.

The source housing is provided with a supply cable which houses theoptical fibers, electrical signals and supplies. This is shown in FIGS.5A-D. FIGS. 5A and 5B show the plan and side view respectively of thesource housing 20 aligned with the Z axis. FIGS. 5C and 5D show the planand side view respectively of the source housing aligned with the Xaxis. The supply cable 60 transmits forces due to its bending onto thesource housing 20 which may result in the source housing not sittingsquarely on the kinematic seat 16. It is therefore desirable to minimisethe force due to the bending of the cable 60.

The supply cable 60 is provided with a cable mounting block 62 which maybe attached to the base plate 10. The mounting block can be clipped intovarious locations on the base plate 10 depending upon the orientation ofthe source housing 20. The position of the cable mounting block 62 onthe base plate is defined by a location seat which could be kinematicand is held in position by magnets (not shown).

The cable mounting block 62 has a plurality of angled faces, such thatin different orientations of the source housing 20, different faces ofthe cable mounting block may be clipped onto the base plate 10, by wayof a respective seat, e.g. kinematic seat on that face.

The position of the location seats and the angles of the faces of thecable mounting block 62 ensures that minimal and equal forces from thecable are transmitted to the source housing for each orientation of thesource housing.

In the present embodiment the base plate is provided with a controlledlowering platform so that the source block is lowered onto thekinematics in controlled way. Use of a controlled lowering platform hasthe advantage that the source housing is gently lowered onto thekinematics ensuring an accurate repeatable location. It also minimisesdamage to the kinematic elements.

FIG. 6A shows a first embodiment of the controlled lowering platform. Alifting platform 64 is provided onto which the source housing 20 may beplaced. This is separated from the base plate by a rotatable disc 66.Ball bearings 68 are located between the disc 66 and the base plate 10and between the disc 66 and the lifting platform 64 to allow rotation ofthe disc 66. The surface of the disc 66 is provided with tapered groovesinto which the ball bearings 68 are seated. When the ball bearings areseated in the wide portion of the groove, the lifting platform 64 is inits lowered position. However as the disc 66 is rotated, the groovepresents its narrower portion to the ball bearing 68 resulting in thelifting platform 64 being raised. By moving the disc 66 in the oppositedirection, the lifting platform 64 may gently be lowered.

A damper 70 is provided to smooth the movement of the lifting platform64. The damper 70 may be provided on a lever 72 which is used to rotatethe disc 66. Alternatively the damper 70 may be located between the baseplate 10 and the lifting platform 64, as shown in FIG. 6B.

A second embodiment of the controlled lowering platform is illustratedin FIGS. 6C and 6D. In this embodiment, the lifting platform 64 isprovided with a downwardly dependent cylinder 74 with a threaded outersurface. The central disc is replaced by a ring 76 with a threaded innersurface. Rotation of the ring 76, using the lever 72 will result in thelifting platform 64 being raised by rotation in one direction and thelifting platform being lowered in the opposite direction.

As in the previous embodiment, a damper 70 may be provided on the lever72 as shown in FIG. 6D or between the base plate 10 and the liftingplatform 64, as shown in FIG. 6C.

A third embodiment of the controlled lowering platform is illustrated inFIGS. 6E, 6F and 6G. In this embodiment the lifting platform 64 issupported by a pair of parallel springs 80, 82. Both springs 80, 82 areconnected to a fixed part of the platform (not shown) at points 84, 86,88 on their outer surfaces and to the moveable platform 64 at theirinner surfaces.

A rod 89 is provided with a cam 94 at one end which abuts the upperspring 80 and a lever 96 at its other end. The rod 89 is rotatable aboutbearings 90, 92 in the fixed surface of the platform (not shown).Rotation of the lever 96 causes rotation of the rod 89 and cam 94. Asthe cam 94 abuts the upper spring 80, it raises or lowers the innersurface of the upper spring 80 as it rotates and thereby also raises andlowers the lifting platform 64 which is attached to the inner surface ofthe spring 80.

Use of a pair of parallel springs 80, 82 results in parallel movement ofthe lifting platform 64, so that even though the cam is located on oneside of the spring 80, the lifting platform 64 is raised and loweredwithout tilting.

In all three embodiments, whether the lifting platform has a rotationalor linear movement, the mechanisms allow the movement of the liftingplatform to be highly repeatable so that each time the source housing islowered onto the kinematics, it is lowered accurately to the sameposition.

The lifting platform of the controlled lowering platform may also beprovided with a set of location elements 97, with a corresponding set oflocation elements 98 on the source housing 20, as illustrated in FIG.6H. These location elements 97, 98 act to correctly position the sourcehousing 20 on the lifting platform 64 so that when the platform 64 islowered, the kinematic elements 93 on the source housing 20 arepre-aligned with kinematic elements 95 on the base plate 10 and thesource housing 20 may therefore be lowered correctly onto the base platekinematics. These location elements 97, 98 on the lifting platform 94and source housing 20 may be less accurate than the location kinematics93, 95 between the source housing 20 and base plate 10. The locationelements 97, 98 on the source housing and lifting platform therebyreceive most of the wear and thus protect the kinematic elements 93, 95on the source housing 20 and base plate 10.

As described earlier, the source housing is mounted on a base platewhich is in turn mounted onto the machine table. The base plate must bealigned with the X-Y plane and this is normally achieved by mounting iton an accurately horizontal machine bed. However if the machine bed isnot accurately horizontal, then adjustment of the base plate isrequired.

FIGS. 7 to 20 illustrate a base plate provided with an adjustmentmechanism which allows for tilt adjustment about both X and Y axes androtation about the Z axis. The adjustable base plate will now bedescribed in more detail with reference to these figures.

FIGS. 7, 8 and 9 show top, side and isomeric views of the base plate 10respectively. The base plate comprises a lower plate 110 and an upperplate 112 which is moveable relative to the lower plate. The upper andlower plates may be connected by means (not shown) which allow relativemovement between them, such as magnetic or spring means.

First and second tilt adjusters 100, 102 are provided on the base plateto enable adjustment of the tilt of the upper plate about the X and Yaxes respectively. FIG. 10 shows a cross section of the first tiltadjuster 100. A pair of rollers 114, 116 is provided in the upper plate112 and a pair of rollers 118, 120 is provided in the lower plate 110. Aball 122 is located between the upper and lower plates and is in contactwith both pairs of rollers. The pair of rollers 114, 116 located in theupper plate 112 are parallel to one another. However the pair of rollers118, 120 located in the lower plate 110 are non parallel. If the ball122 is moved along the rollers 118, 120 towards the narrower end, theball 122 will be pushed upwards and will in turn push the upper plate112 upwards. If the ball 122 is moved in the opposite direction towardsthe wider end, the ball 122 will be lowered and in turn the upper plate112 will be lowered. As shown in FIGS. 7 and 9, an adjustment screw 124is provided to alter the position of the ball 122 within the firstadjustment device 100.

As shown in FIG. 10, the pair of rollers 114, 116 in the upper plate 112provide a kinematic seating for a kinematic element 128 of the sourcehousing 20 and an element 130 is located in contact with and in a fixedposition relative to the pair of rollers 118, 120 in the lower plate 110to connect with the machine table 11.

FIG. 11 shows a cross section of the second tilt adjuster 102. Asbefore, each of the upper and lower plates 112, 110 is provided with apair of rollers 214, 216 and 218, 220 respectively, which locateskinematic elements 228 and 230 in contact with the source housing 20 andmachine table 11 respectively. As before, element 230 is in contact withand in a fixed position relative to rollers 218, 220. However, thesecond tilt adjuster 102 differs from the first 100 in that a plate 232is provided beneath the pair of parallel rollers 214, 216 in the upperplate 112. The ball 222 between the upper and lower plates 112, 110 isthus in contact with the pair of rollers 218, 220 beneath it and theplate 232 above it. As before, adjustment of the position of ball 222using the adjustment screw 126 raises or lowers the upper plate 112directly above it.

At a third location 104, another ball 322 is provided between the upperand lower plates 112, 110 sandwiched between upper and lower pairs ofrollers. FIG. 12 shows a cross section of this arrangement. As beforeboth of the upper and lower plates 110, 112 are provided with a pair ofrollers, 314, 316 and 318, 320 respectively, and the ball 322 is incontact with both pairs of rollers. Ball 322 is in a fixed position withrespect to rollers 314, 316 and ball 220 is in a fixed position withrespect to rollers 318, 320. In this case both pairs of rollers areparallel and the ball 322 is not provided with an adjustment screw.

To adjust the tilt of the base plate 10 about the X axis, the adjustmentscrew 124 of the first tilt adjuster 100 is turned. This will eitherpush the ball 122 and thus the upper plate 112 upwards or downwards,depending on the direction it is turned. As the adjustment screw 124 ofthe first tilt adjuster 100 is turned, the upper plate 112 will pivotabout the ball 222 of the second tilt adjuster 102 and the ball 322 inthe third location 104.

To adjust the tilt of the base plate 10 about the Y axis, the adjustmentscrew 126 of the second tilt adjuster 102 is turned. As described above,this will either push the ball 222 and thus the upper plate 110 upwardsor downwards. As the adjustment screw 126 of the second tilt adjuster102 is turned, the upper plate 110 will pivot about the ball 122 of thefirst tilt adjuster 100 and the ball 322 in the third location 104.

The base plate 10 also enables rotation of its upper plate 112 about theZ axis. A rotation adjustment device 106 is provided for this purpose. Across section of the rotation adjustment device 106 is shown in FIG. 13.

At the rotation adjustment device 106, the upper plate 112 is providedwith a cut out 140 and a portion 142 of the lower plate 110 extendsupwards into the space provided by the cut out 140. In this manner theupper and lower plates 112, 110 are provided with adjacent substantiallyvertical walls 144, 146. As shown in FIG. 13, the substantially verticalwall 144 of the lower plate 110 is provided with a pair of rollers 150,152. The substantially vertical wall 146 of the upper plate 112 isprovided with a plate 154. A ball 156 is in contact with both the pairof rollers 150, 152 and the plate 154. As in the first and second tiltadjusters 100, 102, the rollers 150, 152 are not parallel. If the ball156 is moved along the rollers 150, 152 towards the narrower end, theball 156 will be pushed away from the wall 144 of the lower plate 10 andwill in turn push away the wall 146 of the upper plate 112. The upperplate 112 is thereby rotated relative to the lower plate 110. By movingthe ball 156 in the opposite direction, i.e. towards the wider end, theupper plate 112 will rotate relative to the lower plate 110 in theopposite direction. As before, an adjustment screw 127 is used to alterthe position of the ball 156 on the rollers 150, 152.

When the upper plate 112 is rotated, it interacts with the balls androllers in the first and second tilt adjustment devices 100, 102 and thethird location 104 in the following way. At the first tilt adjustmentdevice 100, the parallel rollers 114, 116 in the upper plate 112 mayslide over the ball 122 in the direction of the nominal center line ofthe rollers, or may rotate about the ball 122. At the second tiltadjustment device 102, the plate 232 of the upper plate 112 slides overthe ball 222 and therefore does not constrain rotational movement of theupper plate 112. At the third location 104, parallel rollers 314, 316 inthe upper plate slide over the ball 322 in the direction of the nominalcenter line of the rollers or the rollers rotate about the ball 322.FIG. 14 shows the movement of the upper plate 112 about each of theballs 122, 222, 322 of the first and second tilt adjustment devices 100,102 and the third location 104 during rotation.

As the balls 122, 222 of the first and second tilt adjustment devices100, 102 remain stationary with respect to the rollers 118, 120, 218,220 in the lower plate 110 and ball 322 of the third location 104remains stationary with respect to the rollers 314, 316 in the upperplate 112, rotation of the upper plate 112 has no effect on the tiltadjustment of the upper plate.

In the above embodiment, the rollers 118, 120 in the lower plate 110 ofthe first and second tilt adjustment devices 100, 102 and the rollers150, 152 of the rotation adjustment device 106 are non parallel suchthat one end of each pair is closer together than the other end. Thiscauses the ball as it is moved along the rollers to be raised as itapproaches the ends closer together or to be lowered as it approachesthe ends further apart.

By varying the angle of the rollers about their nominal center line, itis possible to vary the amount of the height lift of the ball for agiven distance travelled along the rollers. This has the advantage thatit is therefore possible to adjust the sensitivity of the base plate byaltering the angle of the rollers.

FIG. 15 shows a plan view of the non-parallel rollers 118, 120. Thiseffect can be achieved by alternative means, for example as shown inFIG. 16, parallel rollers 160, 162 are set at an angle from the lowerplate 110, so that the ball 164 is moved up and down a slope as it ismoved along the rollers. FIG. 17 shows a pair of tapered parallelrollers 164, 166 with one end of each roller being wider than the otherend.

In an alternative embodiment of the invention, the ball 322 and pairs ofparallel rollers 314, 316, 318, 320 located at the third location 104are replaced with an additional tilt adjustment device, of the same typeas the first tilt adjustment device. This enables the height of theupper plate 112 along the Z axis to be altered, as now the height can beindividually adjusted about all three tilt adjustment points.

In each of the tilt adjustment devices and the rotation adjustmentdevice, the balls are biased towards the adjustment device. FIGS. 18, 19and 20 illustrates the plan, end and perspective views respectively of aspring used to bias the ball towards the adjustment device. The spring170 comprises a slide 172 which is located between the upper and lowerplates 112, 110. A surrounding plate 174 is provided which defines theboundaries of movement of the slide 172. The surrounding plate isattached to the bottom of the upper plate 112. Both the slide 172 andsurrounding plate 174 may be made by a chemi-etch process from the samesheet which ensures that they are the same thickness. This ensures goodtolerances which provides a good slide mechanism.

One end of the slide 174 is provided with three tabs 176, 178, 180. Oneof the tabs 180 protrudes upwards from the middle of the end of theslide 174 and abuts a ball 182 of an adjustment device. The remainingtwo tabs 176, 178 protrudes downwards from either side of the end of theslide 174 and abut springs 184, 186 located in channels 188,190 in theupper plate 112. The springs 184, 186 extend between one end of thechannels 188, 190 and the protruding tabs 176, 178 and thereby exert aforce to bias the slide 172 towards the adjustment device 192. As theslide 172 is pushed towards the adjustment device 192 by the springs184, 186, the tab 180 pushes the ball 182 towards the adjustment device192.

An advantage of the adjustable base plate of the present invention isthat the balls and rollers are in-line between the table, base plate andsource housing, i.e. there is a direct path through the kinematicelements. For example, as shown in FIG. 10, the first tilt adjustmentdevice 100 has a direct path from source housing 20 through kinematicelement 128, rollers 114, 116, ball 112, rollers 118, 120, element 130to table 11. As shown in FIG. 11, the second tilt adjustment device 102has a direct path from source housing 20 through kinematic element 228,rollers 214, 216, plate 232, ball 222, rollers 218, 220, element 230 totable 11. FIG. 21 illustrates a prior art arrangement in which thekinematics between each part are offset. This has the disadvantage thatany distortion of the base plate, e.g. due to thermal bowing, will causea lever effect on the housing. In the present invention with a directpath through the balls and rollers, distortion of the plate has noeffect on the position of the housing. The balls and rollers are made ofa hard material such as steel or tungsten carbide.

1. An apparatus for adjusting the angle of an object about an axismounted on a surface comprising: an upper plate onto which the object ismounted and a lower plate which in turn is mounted onto the surface; atrack located on one of the upper and lower plates; at least one elementlocated on the other of the upper and lower plates; a member locatedbetween the upper and lower plates, the member being in contact with theat least one track and the at least one element; wherein the track isarranged such that when the member is moved in a first direction, themember is raised and causes the plates to move apart and wherein whenthe member is moved in a second opposite direction, the member islowered and causes the plates to move together; wherein one of the atleast one element and the track in the upper plate is part of a mountfor the object and the other of the track and the at least one elementof the lower plate is part of a mount for the surface, thereby forming adirect path from the object to the surface through the tracks, membersand elements.
 2. The apparatus for adjusting the angle of an objectaccording to claim 1, wherein the track comprises a pair of non-parallelrollers.
 3. The apparatus for adjusting the angle of an object accordingto claim 1, wherein the track comprises a pair of parallel rollers whichare positioned at an angle from the plane of the upper or lower plate inwhich they are located.
 4. The apparatus for adjusting the angle of anobject according to claim 1, wherein the track comprises a pair ofrollers and wherein each roller in the pair of rollers is tapered. 5.The apparatus for adjusting the angle of an object according to claim 1,wherein the at least one element comprises a pair of parallel rollers.6. The apparatus for adjusting the angle of an object according to claim1, wherein the at least one element comprises a plane surface.
 7. Theapparatus according to claim 1, wherein the member comprises a ball. 8.An apparatus for adjusting the angle of an object about an axis mountedon a surface comprising: an upper plate onto which the object is mountedand a lower plate which in turn is mounted onto the surface; at leastone track located on one of the upper and lower plates; a least onemember located between the upper and lower plates, the member being incontact with the at least one track in the upper or lower plates;wherein the at least one track is arranged such that when thecorresponding member is moved in a first direction, the member is raisedand causes the plates to move apart and wherein when the member is movedin a second opposite direction, the member is lowered and causes theplates to move together; wherein a track and member is provided betweenadjacent substantially vertical surfaces of the upper and lower platessuch that the upper plate may be rotated about the axis perpendicular tothe plane of the lower plate.
 9. The apparatus for adjusting the angleof an object according to claim 8, wherein the apparatus is providedwith at least two tracks and members to adjust the angle of the upperplate relative to the plane of the lower plate and one track and memberto adjust the angle of the upper plate about the axis perpendicular tothe plane of the lower plate, wherein the tracks used to adjust theangle of the upper plate relative to the plane of the lower plate arelocated in the lower plate so that during rotation of the upper plate,the elements in the upper plate may slide or rotate over the members andthereby allow the upper plate to be rotated independently of theadjustment of the angle of the upper plate relative to the plane of thelower plate.
 10. The apparatus for adjusting the angle of an objectaccording to claim 8, wherein two sets of tracks and members and a pivotmay be provided to allow adjustment of the angle of the upper platerelative to the plane of the lower plate.
 11. The apparatus foradjusting the angle of an object according to claim 8, wherein threesets of tracks and members may be provided to allow adjustment of theangle of the upper plate relative to the plane of the lower plate and inaddition allow adjustment of the height of the upper plate relative tothe lower plate.
 12. The apparatus for adjusting the angle of an objectabout an axis mounted on a surface according to claim 8 wherein themember comprises a ball.